The present invention relates to oil and grease seal units and, more particularly, to radially acting seals which include a relatively stiff mounting portion and a relatively flexible elastomeric sealing lip portion which is adapted to surround or be surrounded by a relatively movable machine member or element to prevent passage of fluid, such as oil or the like, axially along the shaft to the exterior of the region to be sealed. According to the present invention, a novel form of pumping element is provided whereby a strong pumping or oil return action from the exterior of the sealed region to the interior thereof may be accomplished by the provision of generally helically disposed, rib-like pumping elements lying on one frusto-conical surface of the sealing lip. The pumping elements are disposed at an angle both to the direction of shaft rotation and to a shaft axis, and are arranged to blend into the intended area of contact between the seal lip and the shaft, that is, the static lip formed by the convergence of inner and outer frusto-conical surfaces.
In the past, use of helical pattern ribs or vanes as pumping elements has been known, and these elements are generally desirable for certain applications insofar as they provide a pumping action to return oil from the dry side of the sealing lip to the interior of the region to be sealed. In the use of typical shaft seals, the contact pattern made by the seal band on the shaft with which the seal is associated must be continuous in order to provide a proper static seal. As wear occurs, however, the configuration of the static lip contact pattern changes, and the point at which the pumping elements meet the primary seal band area is also subject to change by reason of wear, often with change in the pumping rate.
Also, in the past, the primary or static lip portion of most oil seals was formed by a raised annular rib formed by the junction of one of the frusto-conical surfaces and by a surface of increased steepness on the other frusto-conical surface. In such constructions, the pumping elements were of constant height throughout their extent and intersected the offset static lip or primary lip at a predetermined angle. This configuration of primary lip, while believed necessary for good static sealing performance, was of reduced cross section and hence subject to rapid wear. The steep angle of intersection between the pumping elements and this lip often caused a condition wherein the pumping elements caused lifting of the primary sealing lip area from the shaft or diminished the radial force of the seal band adjacent the point of intersection between the seal band and the inner ends of the pumping elements. Accordingly, prior art seals providing good pumping action were often deficient in static sealing characteristics. Furthermore, seals showing good primary seal characteristics often were subject to rapid wear and/or rapid change in pumping capacity.
Accordingly, in view of the foregoing disadvantages of certain prior art seals utilizing inclined pumping elements, an object of the present invention is to provide an improved seal with a pumping action.
Another object is to provide a seal having a primary seal bond formed merely by the junction of two frusto-conical surfaces and having a plurality of pumping elements with one radially extreme end thereof blending into this area.
Another object is to provide a seal having pumping elements or vanes of varying depth throughout their extent.
A still further object is to provide a seal which includes pumping elements having working edges which are substantially straight and which extend between circumferentially spaced apart points on one seal surface.
A further object is to provide a simplified method of making seal molding apparatus and of making seals with such apparatus.
Another object is to provide a seal wherein the pumping ribs, vanes or elements, when viewed in elevation, approach the primary lip area substantially at a tangent thereto.
A still further object is to provide a seal having improved dynamics and static seal performance in relation to generally similar but less effective prior art seals.
The above enumerated objects and others which are inherent in the invention are achieved by providing a seal having a mounting portion and a fexible sealing lip wherein the lip includes a pair of convergent frusto-conical portions meeting to define a seal band and respectively facing the interior and exterior of a region to be sealed, and having a plurality of pumping elements lying on the surface facing the exterior of the region, each of the elements having a pair of side faces meeting to define a working edge, which is substantially straight and which extends between two radially and axially offset points on the surface which points are also spaced apart from each other by an angle measured parallel to the plane of rotation of a shaft associated in use with the seal. Preferably, the working edge blends into the frusto-conical surface portion of which the edge forms a part.
The manner in which these objects and advantages are achieved in practice will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings, wherein like reference numerals indicate corresponding parts throughout.